There is a long felt need for an economically viable process to manufacture VAM from acetic acid without utilizing independently sourced ethylene. VAM is an important monomer in the production of polyvinyl acetate and polyvinyl alcohol products among other important uses. Due to fluctuating natural gas and crude oil prices contributing to variations in the cost of conventionally produced petroleum or natural gas-sourced ethylene, an important feedstock used in the manufacture of VAM, the need for alternative cost-effective sources of ethylene in order to produce VAM becomes all the greater.
It has now been found that VAM can be produced without utilizing independently sourced ethylene. For example, it is well known that synthesis gas can be reduced to methanol, which is in fact one preferred way to manufacture methanol. Methanol thus formed can then be converted selectively to acetic acid under catalytic carbonylation conditions which is a preferred process for the manufacture of acetic acid. The acetic acid thus formed then can be selectively converted to ethylene under suitable catalytic conditions. Although there are no known preferred processes for such a conversion, the prior art does provide certain processes for such a conversion of acetic acid to ethylene albeit at low conversions and yields thus making it industrially unsuitable.
For instance, it has been reported that ethylene can be produced from various ethyl esters in the gas phase in the temperature range of 150-300° C. over zeolite catalysts. The types of ethyl esters that can be employed include ethyl esters of formic acid, acetic acid and propionic acid. See, for example, U.S. Pat. No. 4,620,050 to Cognion et al., where selectivity is reported to be acceptable.
U.S. Pat. No. 4,270,015 to Knifton describes obtaining ethylene involving a two-step process in which a mixture of carbon monoxide and hydrogen (commonly known as synthesis gas (syngas)) is reacted with a carboxylic acid containing 2 to 4 carbon atoms to form the corresponding ethyl ester of said carboxylic acid which is subsequently pyrolyzed in a quartz reactor at elevated temperatures in the range of about 200° to 600° C. to obtain ethylene.
U.S. Pat. No. 4,399,305 to Schreck describes obtaining high purity ethylene from ethyl acetate employing a cracking catalyst composed of a perfluorosulfonic acid resin commercially sold under the trademark NAFION® by E.I. DuPont de Nemours & Co.
Once ethylene has been produced, further processing with acetic acid is required for conversion to VAM as demonstrated in U.S. Pat. No. 6,696,596 to Herzog et al., incorporated herein by reference in its entirety, which indicates that it is well known to manufacture VAM in a reaction in the gas phase with acetic acid and oxygen or oxygen containing gasses over fixed-bed catalysts.
Additional examples of the manufacture of VAM from ethylene and acetic acid are set forth in U.S. Pat. No. 6,040,474 to Jobson et al. which describes the manufacture of acetic acid and/or vinyl acetate using two reaction zones wherein the first reaction zone comprises ethylene and/or ethane for oxidation to acetic acid with the second reaction zone comprising acetic acid and ethylene with the product streams being subsequently separated thereby producing vinyl acetate. See U.S. Pat. No. 6,476,261 to Ellis et al. which describes an oxidation process for the production of alkenes and carboxylic acids such as ethylene and acetic acid which are reacted to form vinyl acetate demonstrating that more than one reaction zone can be used to form the vinyl acetate.
From the foregoing it is apparent that existing processes do not have the requisite selectivity to ethylene nor does the existing art indicate starting materials other than acetic acid which are expensive and/or intended to produce products other than ethylene.
The present invention utilizes ethylene derived from acetic acid to make VAM in an integrated process, providing alternate synthetic routes which may be utilized for more cost effective production.